María Luisa Lozano

Emerging evidence shows the crucial role of inflammation (particularly NF‐κB pathway) in the development and progression of myelofibrosis (MF), becoming a promising therapeutic target. Furthermore, tailoring treatment with currently available JAK inhibitors (such as ruxolitinib or fedratinib) does not modify the natural history of the disease and has important limitations, including cytopenias. Since recent studies have highlighted the role of miR‐146a, a negative regulator of the NF‐κB pathway, in the pathogenesis of MF; here we used miR‐146a −/− (KO) mice, a MF‐like model lacking driver mutations, to investigate whether pharmacological inhibition of JAK/STAT and/or NF‐κB pathways may reverse the myelofibrotic phenotype of these mice. Specifically, we tested the JAK1/2 inhibitor, ruxolitinib; the NF‐κB inhibitor via IKKα/β, BMS‐345541; both inhibitors in combination; or a dual inhibitor of both pathways (JAK2/IRAK1), pacritinib. Although all treatments decreased spleen size and partially recovered its architecture, only NF‐κB inhibition, either using BMS‐345541 (alone or in combination) or pacritinib, resulted in a reduction of extramedullary hematopoiesis, bone marrow (BM) fibrosis and osteosclerosis, along with an attenuation of the exacerbated inflammatory state (via IL‐1β and TNFα). However, although dual inhibitor improved anemia and reversed thrombocytopenia, the combined therapy worsened anemia by inducing BM hypoplasia. Both therapeutic options reduced NF‐κB and JAK/STAT signaling in a context of JAK2V617F‐driven clonal hematopoiesis. Additionally, combined treatment reduced both COL1A1 and IL‐6 production in an in vitro model mimicking JAK2 ‐driven fibrosis. In conclusion, NF‐κB inhibition reduces, in vitro and in vivo, disease burden and BM fibrosis, which could provide benefits in myelofibrosis patients.